Polyethylenglycol (PEG) is widely used as a water soluble carrier for polymer-drug conjugates. PEG is undoubtedly the most studied and applied synthetic polymer in the biomedical field [Duncan, R. Nature Rev. Drug Discov. 2003, 2, 347-360]. As an uncharged, water-soluble, nontoxic, nonimmunogenic polymer, PEG is an ideal material for biomedical applications. Covalent attachment of PEG to biologically active compounds is often useful as a technique for alteration and control of biodistribution and pharmacokinetics, minimizing toxicity of these compounds [Duncan, R. and Kopecek, J., Adv. Polym. Sci. 57 (1984), 53-101]. PEG possesses several beneficial properties: very low toxicity [Pang, S. N. J., J. Am. Coil. Toxicol, 12 (1993), 429-456], excellent solubility in aqueous solutions [Powell, G. M., Handbook of Water Soluble Gums and Resins, R. L. Davidson (Ed.), Ch. 18 (1980), MGraw-Hill, New York], and extremely low immunogenicity and antigenicity [Dreborg, S, Crit. Rev. Ther. Drug Carrier Syst., 6 (1990), 315-365]. The polymer is known to be non-biodegradable, yet it is readily excretable after administration into living organisms. In vitro study showed that its presence in aqueous solutions has shown no deleterious effect on protein conformation or activities of enzymes. PEG also exhibits excellent pharmacokinetic and biodistribution behavior. [Yamaoka, T., Tabata, Y. and Ikada, Y., J. Pharm. Sci. 83 (1994), 601-606].
Over last three decades, some of promising drug carriers that have been investigated in systemic delivery systems includes liposomes, polymeric nanoparticles, polymeric micelles, ceramic nanoparticles and dendrimers (Cheman et al. Drug. Dev. Ind. Pharm, 26: (2000) 459-463; Lian and Ho. J. Pharm. Sci, 90 (2001) 667-680; Adams et al. Pharm. Sci, 92 (2003) 1343-1355; Na et al. Eur. J. Med. Chem, 41 (2006) 670-674; Kaur et al. J. Control, Rel, 127 (2008) 97-109). Systemic drug delivery can be achieved by intravenous or intraperipheral injection and therefore is non-invasive. The drugs may be administered repeatedly as needed. However, in order to achieve therapeutic concentrations at the target site, systemic administration requires large dosages with relatively high vehicle contents which may cause side effects such as allergic reactions [“Cremophor-based paclitaxel ‘chemo’ drug triggers fatal allergic reactions,” The Medical News. 9 Jun. 2009].
In the design of safe and biocompatible delivery systems, several important factors must be taken into account including high solubilization properties and retaining power of the carrier and appropriate surface characteristics to permit interactions with potential targeting tissue sites or cell membrane permeations.
The important role of sugars in many specific interactions in living systems is well recognized. Large molecular weight carriers such as proteins or liposomes can be modified with sugars for specific drug delivery (Monsigny M, Roche A C, Midoux P and Mayer R., Adv Drug Delivery Rev., 14 (1994):1-24; Palomino E. Adv Drug Delivery Rev., 13 (1994)311-323]. Lipid-sugar particles have been used for drug delivery to the brain for providing prolonged duration local anesthesia when injected at the sciatic nerve in rats [Kohane D S, Lipp M, Kinney R., Lotan N, Langer R., Pharm. Res. 17 (2000) 1243-1249]. Since sugar-lipids are composed of materials that occur naturally in the human body suggests potential advantages over some other polymer-based controlled-release terms of biocompatibility [Kohane D S, Lipp M, Kinney R, Anthony D, Lotan N, Langer R., J. Biomed. Mat. Res. 59 (2002) 450-459; Menei P, Daniel V, Montero-Menei C, Brouillard M, Pouplard-Barthelaix A, Benoit J P., Biomaterials, 14 (1993) 470-478]. Lipid-sugars have a good biocompatibility as shown by the results of the in vitro and in vivo studies [Kohane D S, Lipp M, Kinney R, Anthony D, Lotan N, Langer R., J. Biomed. Mat. Res. 59 (2002) 450-459].
Narrow molecular weight distribution of drug delivery polymers is crucially important for biomedical applications, especially if used for intravenous injections. For instance, PEG-8 Caprylic/Capric Glycerides are mixtures of monoesters, diesters, and triesters of glycerol and monoesters and diesters of polyethylene glycols with a mean relative molecular weight between 200 and 400. Partially due to allergic reactions observed in animals, the application of PEG-8 CCG for many water-insoluble drugs was restricted and a dose limit of approximately 6% of PEG-8 CCG was used for human oral drug formulations.